Raman cooling and heating of two trapped Ba+ ions

We study cooling of the collective vibrational motion of two 138Ba+ ions confined in an electrodynamic trap and irradiated with laser light close to the resonances S_1/2-P_1/2 (493 nm) and P_1/2-D_3/2 (650 nm). The motional state of the ions is monitored by a spatially resolving photo multiplier. Depending on detuning and intensity of the cooling lasers, macroscopically different motional states corresponding to different ion temperatures are observed. We also derive the ions' temperature from detailed analytical calculations of laser cooling taking into account the Zeeman structure of the energy levels involved. The observed motional states perfectly match the calculated temperatures. Significant heating is observed in the vicinity of the dark resonances of the Zeeman-split S_1/2-D_3/2 Raman transitions. Here two-photon processes dominate the interaction between lasers and ions. Parameter regimes of laser light are identified that imply most efficient laser cooling.Comment: 8 pages, 5 figure

Grassland management in Germany: effects on plant diversity and vegetation composition

The vast majority of European grasslands strongly depend on the regular removal of aboveground biomass by agricultural land use, mostly grazing or mowing or a combination of both. These specific management schemes have strong influence on plant diversity and vegetation composition, depending on their particular characteristics and their intensity. For example, the presence or absence of fertilization will favour some species over others, changing plant communities accordingly. Additionally, the farmer's choice of a specific management scheme will also depend on the abiotic site conditions. This leads to a complex set of associated factors potentially affecting the structure and diversity of grasslands. In this study, we compiled a unique dataset of 169 differently managed grasslands (in total 202 plots), which were sampled in five regions across Germany. For each plot, we documented management characteristics, measured plant diversity and functional group composition, recorded endangered species according to red lists, and calculated Ellenberg indicator values. We assessed patterns in vegetation composition and diversity in relation to the particular management scheme, which was categorized as meadow, meadow with autumn or winter grazing (with mowing as predominant management), mown pasture (where mowing and grazing are used at roughly equal intensity), seasonal pasture (with grazing as predominant management) and year-round pasture. Our study showed that grasslands of different management schemes significantly differed in diversity, structure and functional composition. However, it also became obvious that vegetation composition was not strictly distinguished by management alone. Local and regional characteristics such as soil conditions, size of the grassland species pool or land-use history, often played a more prominent role than land use alone. Assumingly, the interplay of those local and regional characteristics with the pro portion of grazing and mowing at a particular site inhibit clear differences among our predefined management schemes. Nevertheless, species richness was the lowest in year-round pastures, moderate in meadows and highest in seasonal pastures. In contrast, year-round pastures harboured the highest mean numbers of endangered species. The dependency of a certain management scheme on site-specific environmental factors such as soil fertility, further complicated the clear separation of management effects from those of the environmental background. In summary, modern grassland management strongly shaped grassland vegetation, but today's combination of different management practices complicated the assessment of specific land-use effects on plant diversity. Thus, neither mowing nor grazing turned out to be ``the one and only'' management for nature conservation. Although our results challenge long-term prognoses for future vegetation development under modern grassland management, we clearly showed that low-intensity management and the absence of fertilization promoted plant diversity, with higher values in pastures compared to meadows and mown pastures

Grünlandnutzung in Deutschland: Auswirkungen auf Pflanzendiversität und Vegetationszusammensetzung

The vast majority of European grasslands strongly depend on the regular removal of aboveground biomass by agricultural land use, mostly grazing or mowing or a combination of both. These specific management schemes have strong influence on plant diversity and vegetation composition, depending on their particular characteristics and their intensity. For example, the presence or absence of fertilization will favour some species over others, changing plant communities accordingly. Additionally, the farmer’s choice of a specific management scheme will also depend on the abiotic site conditions. This leads to a complex set of associated factors potentially affecting the structure and diversity of grasslands. In this study, we compiled a unique dataset of 169 differently managed grasslands (in total 202 plots), which were sampled in five regions across Germany. For each plot, we documented management characteristics, measured plant diversity and functional group composition, recorded endangered species according to red lists, and calculated Ellenberg indicator values. We assessed patterns in vegetation composition and diversity in relation to the particular management scheme, which was categorized as meadow, meadow with autumn or winter grazing (with mowing as predominant management), mown pasture (where mowing and grazing are used at roughly equal intensity), seasonal pasture (with grazing as predominant management) and year-round pasture. Our study showed that grasslands of different management schemes significantly differed in diversity, structure and functional composition. However, it also became obvious that vegetation composition was not strictly distinguished by management alone. Local and regional characteristics such as soil conditions, size of the grassland species pool or land-use history, often played a more prominent role than land use alone. Assumingly, the interplay of those local and regional characteristics with the proportion of grazing and mowing at a particular site inhibit clear differences among our predefined management schemes. Nevertheless, species richness was the lowest in year-round pastures, moderate in meadows and highest in seasonal pastures. In contrast, year-round pastures harboured the highest mean numbers of endangered species. The dependency of a certain management scheme on site-specific environmental factors such as soil fertility, further complicated the clear separation of management effects from those of the environmental background. In summary, modern grassland management strongly shaped grassland vegetation, but today’s combination of different management practices complicated the assessment of specific land-use effects on plant diversity. Thus, neither mowing nor grazing turned out to be “the one and only” management for nature conservation. Although our results challenge long-term prognoses for future vegetation development under modern grassland management, we clearly showed that low-intensity management and the absence of fertilization promoted plant diversity, with higher values in pastures compared to meadows and mown pastures.Die meisten mitteleuropäischen Grünlandhabitate sind anthropogen entstanden und hängen von regelmäßiger Nutzung durch Mahd oder Beweidung ab (POSCHLOD et al. 2009). Seit der Intensivierung der Landwirtschaft in den 1950/60er Jahren ist artenreiches Grünland in Nordwest-Europa jedoch stark zurückgegangen, und wird deshalb heute vielerorts streng geschützt (WESCHE et al. 2012). Trotzdem hält europaweit der Trend der Nutzungsintensivierung und -änderung noch immer an (KÜMMERLE et al. 2016), sodass Studien zum Einfluss verschiedener Nutzungstypen auf die Artenvielfalt im Grünland wichtig für den Erhalt dieser Lebensräume sind. Generell wirken sich Beweidung und Mahd unterschiedlich auf die Vegetation aus, da Beweidung selektiv Pflanzen bzw. deren oberirdische Bestandteile schädigt, während Mahd alle Pflanzen einer Wiese in gleichem Maße betrifft (z. B. SOCHER et al. 2012, KLAUS et al. 2013a, b, BOCH et al. 2016, KRUSE et al. 2016). Die Bandbreite an Nutzungstypen und -intensitäten ist allerdings sehr groß und oft werden heutzutage Mahd und Beweidung auf einer Fläche kombiniert, weshalb auch die Einflüsse auf die Artvielfalt und die Artenzusammensetzung vielseitig sind (BLÜTHGEN et al. 2012). In dieser Studie untersuchen wir den Einfluss verschiedener Nutzungstypen (Ganzjahresweiden, Saisonweiden, Mähweiden, Wiesen mit Nachbeweidung im Herbst oder Winter und reine Wiesen) in Interaktion mit abiotischen Standortfaktoren auf die Vegetationszusammensetzung und deren Vielfalt in fünf Regionen Deutschlands. Wir haben 202 Vegetationsaufnahmen in 169 unterschiedlich genutzten Grünlandflächen in fünf verschiedenen Regionen Deutschlands angefertigt: Friesland-Hamburg (Norden), Niederrhein-Westfalen (Nordwesten), Schorfheide-Chorin (Nordosten), Hainich-Dün (Mitte) und Schwäbische Alb (Südwesten), siehe auch Tabelle 1 und Abbildung 1. Die letztgenannten drei Regionen sind Teil des Forschungsprojekts „Biodiversitäts-Exploratorien“ zur Erforschung funktionaler Zusammenhänge zwischen Artenvielfalt, Ökosystemfunktionen und Landnutzung (www.bioversityexploratories.de; FISCHER et al. 2010). Während das Klima im Nordwesten Deutschlands ausgeprägt atlantisch ist, liegt den Untersuchungsgebieten ein klimatischer Gradient mit nach Nordosten zunehmender Kontinentalität zugrunde. Die Untersuchungsgebiete unterscheiden sich zudem hinsichtlich weiterer regionalen Gegebenheiten wie etwa Geologie und Boden (Tab. 1)

Scale‐dependent patterns and drivers of plant diversity in steppe grasslands of the Central Alborz Mts., Iran

Questions: Which are the main environmental drivers of plot scale alpha-diversity and beta-diversity in arid steppes? Do they vary between functional groups and across grain sizes? Location: Central Alborz Mts., N Iran. Methods: We sampled vascular plants in 23 nested-plot series with nine grain sizes from 0.0001 m2 to 1,000 m2 and 334 25-m2 vegetation plots in different vegetation types of natural dry steppe grasslands. To assess beta-diversity, we calculated overall and local z-values of species–area relationships modelled with the power function. As potential drivers of species richness and z-values, we used topographic, edaphic and climatic variables as well as management types. Generalised linear models (GLMs), and generalised linear mixed-effect models (GLMMs) if spatial autocorrelation occurred, were used in a multi-model inference framework to build statistical models. Results: Mean annual temperature was the most important predictor for total species richness and richness of functional groups across grain sizes, with a unimodal relationship for grains of 25–100 m2, but mostly increasing for finer grain sizes. Precipitation of the driest month and cover of gravel were influential drivers at the smallest grains. The explanatory power of regression models increased towards larger grain sizes. The overall z-values showed a high positive relationship with precipitation of the driest month, mean annual temperature and mean soil depth. Conclusions: Related to our more than 3,000-m elevational gradient, mean annual temperature (highly negatively correlated with elevation) was the most influential and consistent driver across functional groups and grain sizes with mostly unimodal relationships for alpha-diversity and a positive effect on beta-diversity. Findings for other drivers were less consistent, and overall the explained variance of our models was relatively low, calling for additional studies to determine whether in the arid grasslands of Iran stochasticity is just higher or there are additional important variables